1. 1. Web Scraping with PHP Matthew Turland September 16, 2008
2. 2. Everyone acquainted?
   • Lead Programmer forsurgiSYS, LLC
   • PHP Communitymember
   • Blog:http://ishouldbecoding.com
3. 3. What is Web Scraping? 2 Stage Process Stage 1 : Retrieval GET/some/resource ... HTTP/1.1 200OK ... Resource with datayou want Stage 2 : Analysis Raw resource Usable data
4. 4. How is it different from... Data Mining Focus in data mining Focus in web scraping Consuming Web Services Web service data formats Web scraping data formats
5. 5. Potential Applications What Data source When Web service is unavailable or dataaccess is one-time only. Crawlers and indexers Remote data search offers nocapabilities for search or data sourceintegration. Integration testing Applications must be tested bysimulating client behavior andensuring responses are consistent with requirements.
6. 6. Disadvantages == vs
7. 7. Legal Concerns TOS TOU EUA Original source Illegal syndicate IANAL!
8. 8. Retrieval GET/some/resource ... sizeof( ) == sizeof( ) if( ) require ;
9. 9. The Low-Down on HTTP
10. 10. Know enough HTTP to... Use one like this: To do this:
11. 11. Know enough HTTP to... PEAR::HTTP_Client pecl_http Zend_Http_Client Learn to use and troubleshoot one like this: Or roll your own! cURL Filesystem+Streams
12. 12.
    • GET /wiki/Main_Page HTTP/1.1
    • Host: en.wikipedia.org
    Let's GET Started methodoroperation URIaddress for thedesiredresource protocol versioninuse by the client headername headervalue request line header more headers follow...
13. 13. Warning about GET In principle: "Let's do this by the book." GET In reality: "' Safe operation '? Whatever." GET
14. 14. URI vs URL 1. Uniquely identifies a resource 2. Indicates how to locate a resource 3. Does both and is thus human-usable. URI URL More info inRFC 3986Sections1.1.3and1.2.2
15. 15. Query Strings http://en.wikipedia.org/w/index.php? title=Query_string&action=edit URL Query String Question markto separate the resource address andquery string Equal signsto separate parameter names and respective values Ampersandsto separateparametername-value pairs. Parameter Value
16. 16. URL Encoding Parameter Value first second this is a field was it clear enough (already)? Query String first=this+is+a+field&second=was+it+clear+%28already%29%3F Also calledpercent encoding . urlencodeandurlencode : HandyPHP URL functions $_SERVER ['QUERY_STRING'] /http_build_query ( $_GET ) More info on URL encoding inRFC 3986 Section 2.1
17. 17. POST Requests Most Common HTTP Operations 1. GET 2. POST ... /w/index.php POST /new/resource -or- /updated/resource GET /some/resource HTTP/1.1 Header: Value ... POST /some/resource HTTP/1.1 Header: Value request body none
18. 18. POST Request Example
    • POST /w/index.php?title=Wikipedia:Sandbox HTTP/1.1
    • Content-Type: application/x-www-form-urlencoded
    • wpStarttime=20080719022313&wpEdittime=20080719022100...
    Blank lineseparates request headers and body Content typefor data submitted via HTML form (multipart/form-data forfile uploads ) Request body ... look familiar? Note : Most browsers have a query string length limit. Lowest known common denominator: IE7 strlen(entire URL) array( 'method' => 'POST', 'header' => 'Content-Type: ' . 'application/x-www-form-urlencoded', 'content' => http_build_query(array( 'var1' => 'value1', 'var2' => 'value2' )) ))); // Last 2 parameters here also apply to fopen() $post =file_get_contents ($uri, false, $context);
19. 26. Streams Resources
    • Language Reference > Context options and parameters
    • • HTTP context options
    • • Context parameters
    • Appendices > List of Supported Protocols/Wrappers
    • • HTTP and HTTPS
    • php|architect's Definitive Guide to PHP Streams (ETA late 2008 / early 2009)
20. 27. pecl_http Examples $http = newHttpRequest ($uri); $http-> enableCookies (); $http-> setMethod (HTTP_METH_POST); // or HTTP_METH_GET $http-> addPostFields ($postData); $http-> setOptions (array( 'httpauth' => $username . ':' . $password, 'httpauthtype' => HTTP_AUTH_BASIC, useragent => 'PHP ' . phpversion(), 'referer' => 'http://example.com/some/referer', 'range' => array(array(1, 5), array(10, 15)) )); $response = $http-> send (); $headers = $response-> getHeaders (); $body = $response-> getBody (); SeePHP Manual for more info.
21. 28. PEAR::HTTP_Client Examples $cookiejar = newHTTP_Client_CookieManager (); $request = newHTTP_Request ($uri); $request-> setMethod (HTTP_REQUEST_METHOD_POST); $request-> setBasicAuth ($username, $password); $request-> addHeader ('User-Agent', $userAgent); $request-> addHeader ('Referer', $referrer); $request-> addHeader ('Range', 'bytes=2-3,5-6'); foreach ($postData as $key => $value) $request-> addPostData ($key, $value); $request-> sendRequest (); $cookiejar-> updateCookies ($request); $request = newHTTP_Request ($otheruri); $cookiejar-> passCookies ($request); $response = $request-> sendRequest (); $headers = $request->getResponseHeader(); $body = $request->getResponseBody(); SeePEAR Manual andAPI Docs for more info.
22. 29. Zend_Http_Client Examples $client = newZend_Http_Client ($uri); $client-> setMethod (Zend_Http_Client::POST); $client-> setAuth ($username, $password); $client-> setHeaders ('User-Agent', $userAgent); $client-> setHeaders (array( 'Referer' => $referrer, 'Range' => 'bytes=2-3,5-6' ); $client-> setParameterPost ($postData); $client-> setCookieJar (); $client-> request (); $client-> setUri ($otheruri); $client-> setMethod (Zend_Http_Client::GET); $response = $client-> request (); $headers = $response-> getHeaders (); $body = $response-> getBody (); SeeZF Manual for more info.
23. 30. cURL Examples Fatal error: Allowed memory size of n00b bytesexhausted (tried to allocate 1337 bytes) in/this/slide.php on line 1 SeePHP Manual ,Context Options , ormy php|architect article for more info. Just kidding. Really, the equivalent cURL code for theprevious examples is so verbose that it won't fit on one slide and I don't think it's deserving of multiple slides.
24. 31. HTTP Resources
    • RFC 2616 HyperText Transfer Protocol
    • RFC 3986 Uniform Resource Identifiers
    • "HTTP: The Definitive Guide" (ISBN 1565925092)
    • "HTTP Pocket Reference: HyperText Transfer Protocol" (ISBN 1565928628)
    • "HTTP Developer's Handbook" (ISBN 0672324547) byChris Shiflett
    • Ben Ramsey's blog series on HTTP
25. 32. Analysis Raw resource Usable data DOM XMLReader SimpleXML XSL tidy PCRE String functions JSON ctype XML Parser
26. 33. Cleanup
    • tidy is good for correcting markup malformations. *
    • String functions and PCRE can be used for manual cleanup prior to using a parsing extension.
    • DOM is generally forgiving when parsing malformed markup. It generates warnings that can be suppressed.
    • Save a static copy of your target, use a validator on the input (ex:W3C Markup Validator ), fix validation errors manually, and write code to automatically apply fixes.
27. 34. Parsing
    • DOM and SimpleXML are tree-based parsers that store the entire document in memory to provide full access.
    • XMLReader is a pull-based parser that iterates over nodes in the document and is less memory-intensive.
    • SAX is also pull-based, but uses event-based callbacks.
    • JSON can be used to parse isolated JavaScript data.
    • Nothing "official" for CSS. Find something likeCSSTidy .
    • PCRE can be used for parsing. Last resort, though.
28. 35. Validation
    • Make as few assumptions (and as many assertions) about the target as possible.
    • Validation provides additional sanity checks for your application.
    • PCRE can be used to form pattern-based assertions about extracted data.
    • ctype can be used to form primitive type-based assertions.
29. 36. Transformation
    • XSL can be used to extract data from an XML-compatible document and retrofit it to a format defined by an XSL template.
    • To my knowledge, this capability is unfortunately unique to XML-compatible data.
    • Use components like template engines to separate formatting of data from retrieval/analysis logic.
30. 37. Abstraction
    • Remain in keeping with the DRY principle.
    • Develop components that can be reused across projects. Ex:DomQuery ,Zend_Dom .
    • Make an effort to minimize application-specific logic. This applies to both retrieval and analysis.
31. 38. Assertions
    • Apply to long-term real-time web scraping applications.
    • Affirm conditions of behavior and output of the target application.
    • Use in the application during runtime to avoid Bad Things (tm) happening when the target application changes.
    • Include in unit tests of the application. Youareusing unit tests, right?
32. 39. Testing
    • Write tests on target application output stored in local files that can be run sans internet during development.
    • If possible/feasible/appropriate, write "live tests" that actively test using assertions on the target application.
    • Run live tests when the target appears to have changed (because your web scraping application breaks).
33. 40. Questions?
    • No heckling... OK, maybe just a little.
    • I will hang around afterward if you have questions, points for discussion, or just want to say hi. It's cool, I don't bite or have cooties or anything. I have business cards too.
    • I generally blog about my experiences with web scraping and PHP at http://ishouldbecoding.com.
    • Thanks for coming!